Information about a stimulus is transmitted within the nervous system by the electrical discharges of neurons. Several different encoding methods have been proposed including a rate‐code, synchrony code and other temporal codes. We have applied information theory to describe the contribution of the different encoding systems in object recognition. The nervous system not only transmits information but is adaptive so that its neuronal properties can be modified by learning to respond to new categories of stimuli. This is a crucial function of the nervous system not only in children but also in adults and its malfunction can lead to a severely disabling mental disease known as Alzheimer’s or senile dementia. Acetylcholine is thought to be a chemical transmitter implicated in learning, attention and in Alzheimer’s disease. In a recent experiment, a